Generally, the angular velocity sensing devices for detecting the angular velocities of inertial bodies have been widely employed as a component of navigation apparatus in the ocean vessels, air planes and the like. At the present, this device has been extended to the navigation apparatus of automobiles, and to the high performance video camera as a hand-oscillation compensating device.
The conventional gyroscope which has been used for the military purposes and for air planes is manufactured by using a plurality of high precision components and through a complicated assembling process, and therefore, a precise performance is possible. However, its manufacturing cost is high, and its bulk is very large, with the result that it cannot be used for the general industries, and for the home power appliances.
Recently, a small gyroscope has been developed by attaching a piezoelectric device to a triangular prism beam, and this is used as a hand-oscillation sensor for a small video camera. Further, in order to overcome the difficulties of the gyroscope having the piezoelectric device, a small gyroscope with an improved cylindrical beam structure has been developed.
However, these two kinds of the small gyroscopes require precisely machined components, and therefore, the manufacture becomes difficult, while the manufacturing cost becomes high. Further, the mentioned two kinds of gyroscope includes a plurality of mechanical components, and therefore, it is difficult to form a circuit integration.
The principle of the gyroscope is as follows. That is, when a rotating inertial body which rotates or oscillates in a first axis direction receives an input of an angular velocity in a second axis direction (which is perpendicular to the first axis direction), the gyroscope detects a Coriolis force which acts in a third axis direction (which is rectangular to the first and second axes direction).
Under this condition, if the forces acting on the inertial body are made to be balanced, then the detection of the angular velocity has to be more precise. Particularly, if the linearity and the band width are to be expanded, a force balancing structure is required.
A conventional microgyroscope related to this technique is illustrated in U.S. Pat. No. 5,747,690, and it is as shown in FIG. 1.
As shown in FIG. 1, an excitation is made to occur in the horizontal direction by utilizing combs 41, and in the same manner, the Coriolis oscillations of a floating mass 50 induced in the perpendicular direction (y axis) can be sensed by sensing electrodes 38.
Under this condition, in the case where an ac voltage is supplied to combs 39, 40, 41 and 42 of both sides of the floating mass 50 so as to make the floating mass 50 oscillate in the direction of the x axis, if an angular velocity is inputted in the direction of the z axis, then the mass is oscillated in the direction of the y axis with the same frequency by the Coriolis force. Under this condition, the oscillation range in the direction of the y axis can be detected based on the relevant oscillation frequency by utilizing the sensing electrodes 38 proportionally to the supplied angular velocity, thereby obtaining the angular velocity signals.
However, in the above described case, the mass oscillates to one side, and therefore, the oscillations are excessively transmitted to the supporting part. As a result, a mechanical loss is resulted, and the exciting oscillation width is affected by the external oscillations.
Further, in the above described microgyroscope, by the strong transmission of the oscillations to the supporting part 31, a negative influence is received to the rise of the sensitivity of the gyroscope, and the linearity is aggravated due to the magnitude of the angular velocity. Consequently, the resolving power of the gyroscope is lowered, and the life expectancy of the gyroscope is shortened.